Update value in DataSet in VB.NET

private void button1_Click(object sender, EventArgs e)
{
    // create a new ds with a table and a column
    DataSet ds = new DataSet();

    ds.Tables.Add("Table1");

    ds.Tables[0].Columns.Add("Magin", typeof(int));

    // populate some test data
    for (int i = 0; i < 100; i++)
    {
        DataRow dr = ds.Tables[0].NewRow();

        dr[0] = i;

        ds.Tables[0].Rows.Add(dr);
    }

    // update the column to a value
    ds.Tables[0].Columns["Magin"].Expression = "4";
}